This invention relates to the treatment of water by the controlled introduction of antibacterial substances and by the control of parameters which affect the effectiveness of the substances. More specifically, this invention relates to an apparatus for controlling the chlorine residual and the pH of water in a swimming pool.
Swimming pools provide a great deal of recreational pleasure. The pleasure derived from a swimming pool is substantially dependent upon the quality of the water in the pool. To assure comfort and safety to swimmers using the pool, it is absolutely essential that the water be properly treated chemically. Chemical treatment of swimming pool water primarily involves two pool water tests-- one for chlorine, the other for pH.
Since its introduction into water treatment, chlorination has become a universally accepted method for active disinfection of water and both public and private swimming pools rely on chlorine to sterilize the pool of bacteria and maintain water purity. A chlorine residual must be maintained in the pool water for effective sterilization. If too little chlorine is supplied to the water, not all bacteria will be removed from the water, and the swimming pool will not be safe for swimming. For this reason chlorine in excess of that required for complete sterilization is generally supplied, resulting in a chlorine residual in the pool water. A good average chlorine residual is 1.0 parts per million (ppm); however the pool may effectively have a residual chlorine level as low as 0.6 ppm or as high as 2.0 ppm.
The retention of chlorine residual in swimming pool water is the key to an effective bacteriacidal function. Chlorine escapes into the atmosphere from the open pool water and is consumed by its sterilizing action in an amount proportional to the level of bacteria present in the swimming pool. The quantity of chlorine required to completely sterilize the water in the swimming pool is referred to as the chlorine demand. Chlorine demand of a pool is affected by several factors. The bather load will affect chlorine demand as each swimmer entering the pool uses some of the chlorine residual. Therefore, more swimmers require more chlorine be added to the pool water. Higher water temperatures tend to exhaust chlorine more rapidly. Rain showers and high winds introduce atmospheric contaminants into the pool and dilute its chemical system, creating a greater demand for chlorine. Direct sunlight accelerates the dissipation of chlorine and foliage such as trees, shrubs, flowers and grass in the pool area contribute algae spores, leaves, pollen and associated wastes which stress the pool's chemical system.
Swimming pools may be chlorinated manually by administering a granular form of organic concentrate directly into the pool, but the most common way to introduce chlorine into the pool water is through a chlorinator. A conventional chlorinator receives a continuous flow of water which passes through a container of chlorine. In the past, it has been necessary to periodically perform a manual test on the pool water to check for proper chlorine supply. The test involves the taking of a sample of pool water by hand and adding an indicator substance which provides an indication of chlorine concentration. The pool side test for chlorine establishes the average demand rate and confirms that the necessary level of chlorine residual for effective bacteria control is being maintained. The pool side test for chlorine is usually made using a conventional test reagent, such as o-toludine. While the test should be run often at periodic intervals, all too often the test is not performed due to forgetfulness or inattentiveness.
Proper pH control is essential to the correct operation of a pool as the microbicidal activity of chlorine is pH dependent. The pH value of the swimming pool water expresses its acid-alkali ratio. A desirable pH range for pool operation is pH 7.4 to pH 7.6, slightly basic. Lower pH values tend to accelerate the loss of chlorine and cause excessive eye irritation, corrosion of metal components and possible etching of the pool's interior. Higher pH values slow the microbicidal function of chlorine and can produce scale formation on the pool interior, piping and heater coils.
In addition, some nitrogen, in the form of ammonia, is in the pool water at all times from sources such as human wastes. Chlorine in the pool water may combine with the nitrogen to form other chemical compounds called "chloramines". The formation of chloramines is accelerated as the pH goes to 7.0 or lower. The formation of such compounds is retarded by keeping the pH in the desired slightly basic range. Chloramines may cause eye discomfort to swimmers using the pool a great deal and extensive chemical treatment may be necessary to remove chloramines from the water, assuring its comfort for swimming.
The most frequent adjustment required is to lower the pH of pool water. Left uncorrected, the water in a swimming pool has a tendency to rise in pH due to the introduction of foreign matter. To lower the pH level, strong liquid acids such as muriatic acid have been used. Strong acids of this type are potentially dangerous and are hazardous when being handled. Acid may be added to swimming pool water in several different ways. One approach is to dump a quantity of acid in the swimming pool periodically. The addition of acid to pool water in this manner does lower pH, but the change is abrupt, causing an excessive loss of chlorine in a broad area where the acid is released. A second approach is to use an acidifier connected into a flow line of the circulation system of the pool to constantly supply acid to the pool. This method can result in the addition of too much acid to the pool, driving the pH below the desired range.
It is apparent that present water treatment methods for swimming pools are extremely haphazard and leave much to be desired from a safety and health standpoint. It is further apparent that coordinated control of both chlorine residual and pH without the continual performance of tests is highly desirable.